feat: implement authentication and database modules with relations and group management

Added new authentication strategies (JWT and GitHub OAuth), guards, and controllers. Implemented database module, schema with relations, and group management features, including CRD operations and person-to-group associations. Integrated validation and CORS configuration.

backend/.gitignore

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+# compiled output
+/dist
+/node_modules
+/build
+
+# Logs
+logs
+*.log
+npm-debug.log*
+pnpm-debug.log*
+yarn-debug.log*
+yarn-error.log*
+lerna-debug.log*
+
+# OS
+.DS_Store
+
+# Tests
+/coverage
+/.nyc_output
+
+# IDEs and editors
+/.idea
+.project
+.classpath
+.c9/
+*.launch
+.settings/
+*.sublime-workspace
+
+# IDE - VSCode
+.vscode/*
+!.vscode/settings.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+
+# dotenv environment variable files
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# temp directory
+.temp
+.tmp
+
+# Runtime data
+pids
+*.pid
+*.seed
+*.pid.lock
+
+# Diagnostic reports (https://nodejs.org/api/report.html)
+report.[0-9]*.[0-9]*.[0-9]*.[0-9]*.json